In the employment of electric ignition systems for initiating explosive charges, nearby radio and radar stations, as well as other sources of radiation, constitute potential risks, since they could give rise to sufficiently powerful induced currents in the ignition wiring to cause accidental initiation of the charges. This is a serious drawback which is inherent in all electric ignition system and because of this drawback, in electrical ignition systems intended for military applications, it has been necessary to incorporate complex anti-disturbance systems, since, in field-service use it cannot be anticipated, as in civilian blasting operations using electrical ignition systems, that all use of radio, radar or other radiation transmitters in the vicinity of the explosion site can be prevented.
It has previously been common to provide electrically initiated blasting cartridges (blasting caps), when necessary, with pyrotechnical delay charges of conventional type. However, electronic delayed action igniters with very good performance as regards precise and well-known ignition intervals and small outside dimensions have recently become available at highly attractive prices.
These electronic delayed action igniters constitute a further argument in favor of choosing an electric instead of a non-electric ignition system in the initiation of explosive charges. However, as soon as an electric ignition system is employed in which the electric wires are of sufficient length to run the risk of induced currents in the wires, there will be the additional requirement of accurate and therefore also complex and expensive disturbance shielding of the entire ignition system.
Consequently, it would in many cases be desirable to have access to a non-electric ignition system which could occur the same exact time lag as the electronic time igniters and which could never be achieved using even the best pyrotechnical delay charge.